Lasers can be considered the ultimate in illumination sources offering both spectral and spatial purity. The light emitting sources emit substantially one wavelength, with diffraction-limited collimation making them orders of magnitude brighter than conventional sources such as UHP lamps, with the option of adding extra emitters without exceeding étendue limitations of any one system. These properties overcome many issues associated with conventional sources and offer opportunities with greater efficiencies in lower cost simpler systems. Some LEDs have similar properties to lasers and may similarly be used as spectral emitters.
To date, laser displays have been of three types. The first utilizes scanning mirrors to deflect a modulated beam in a raster format. See e.g., Symbol Technologies OD Monochrome projector. A second illuminates a conventional, two-dimensional spatial light modulator or panel (e.g., laser illuminated RPTV demonstrated by Mitsubishi at CES 2006), and a third combines the first two using a one dimensional spatial modulator with a single axis deflecting mirror (e.g., GxL projector from Sony). Scanning systems are inherently more unsafe than spatially modulated beams since in the event of the scanning mechanism stopping, a single high intensity laser beam can be directed accidentally into the eye of a viewer. For this reason these systems are typically limited to micro projection systems where laser intensities are modest. Hybrid systems offer the potential of high quality images but invariably suffer from asymmetric spatial performance and require more complex tandem systems.